The present invention relates generally to blow-molded plastic containers and particularly to a blow pin assembly and mold for blow-molding containers from an extruded parison to provide an inclined finish on the container having a uniform wall thickness.
Various methods and apparatus for blow-molding plastic containers are known including apparatus for blow-molding containers from an extruded parison. In such apparatus, a tube-like parison is extruded from an extruder head and as the parison reaches the desired or corrected length, a split or bifurcated mold closes around the parison. The parison is severed above the mold so as to create a small amount of flash, and the mold with the enclosed parison is shuttled to a blowing station. A blow pin is lowered into the open top portion of the parison as it is held in the mold. Once the blow pin is in the correct position, a blowing medium, typically air, is introduced into the parison causing the container to be formed by the parison conforming to the contours of the cavity on the inside of the mold. The two halves or bifurcated portions of the mold then separate from each other leaving the formed container. The mold then proceeds to close on another extruded tubular parison to repeat the process.
As a general rule, the extruded tubular parison has a circularly symmetric wall thickness. The thickness of the wall of the finished container at any point is inversely related to the radius of that point from the axis of the container. That is, as the parison is stretched further before coming in contact with the interior surface of the mold, the wall thickness becomes increasingly thinner. In most circumstances, such a non-uniform thickness as a function of radius is desirable. However, it is sometimes desirable to form a container at least a portion of which has a uniform thickness over a varying radius from the axis of the container. This is particularly true when forming a pouring spout on a container such as a carafe, coffee pot or the like.
It is therefore an object of the present invention to provide a mold and blow pin assembly for blow-molding containers from extruded tubular parisons which provides for a finish of substantially uniform thickness, particularly where that finish is non-symmetric about the axis of the container and where the finish is inclined with respect to a plane normal to the axis of the container.